Bone Remodeling of the Human Mandible during Prenatal Development

MATERIAL AND METHOD: Based on histological serial sections of human fetuses (22-117 mm crown-rump length) the remodeling of the bone surfaces of the fetal mandible was characterized and visualized in 3D reconstructions. RESULTS: In the embryo of 22 mm crown-rump length the mandible was completely covered by cells producing bone apposition, but beginning with the embryo of 25 mm crown-rump length, morphological differentiations of these cells leading to bone modeling were visible. These modeling processes were found to be much more complicated than described in the literature so far. CONCLUSION: Bone growth of the fetal mandible is a complex process comprising not only lingual resorption and buccal apposition. Instead, we found well differentiated remodeling processes, represented by variable portions of apposition, resorption and resting areas seamed by lining cells.     

下颌骨偏斜畸形颏孔区锥形束CT观察分析

目的    应用锥形束CT（CBCT）观察、测量下颌骨偏斜畸形患者颏孔区牙槽骨形态,为正颌外科手术中颏成形术提供参考,减少神经、血管损伤等并发症的发生。方法    选取2014年3月至2015年10月大连市口腔医院收治的下颌骨偏斜畸形成人患者84例,进行CBCT扫描,用InVivo5软件对下颌骨进行三维重建,定位标记点,观察、测量和分析下颌骨颏孔位置及颏管形态,用SPSS17.0软件包对测量结果进行分析。结果    颏孔大部分位于下颌第二前磨牙下方（39.29%）,位于第一前磨牙下方（11.90%）者最少。各测量值在偏斜侧和偏斜对侧的差异无统计学意义,除颏管角度外,性别差异较显著,均为男性大于女性。结论    下颌骨偏斜畸形患者颏孔位置较正常人有一定差异,男女性之间也有所不同,CBCT影像可清晰显示颏管的三维结构、走向以及与邻近结构的关系,可以有效减少或避免手术并发症。     

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??Objective    To observe and measure the mandibular alveolar bone morphology at the area of mental foramen in the patients with mandibular deviation by CBCT to provide reference for genioplasty in orthognathic surgery??so as to reduce the complications such as the injury to nerves and blood vessels. Methods    In this study??84 adults with mandible deviation were selected??CBCT scans were conducted and InVivo 5 software was used to reconstruct the mandible??locate the markers??observe and measure and analyze the position of the mental foramen and the morphology of the mental canal. All the measurements were analyzed with SSPS 17.0 package. Results    The mental foramen was mostly below the second premolar at the mandibular??39.29%????and below the first premolar is the least??11.90%??. There was no significant difference between the oblique side and the contralateral side on all measurement values??in addition to the angle of the mental canal??the gender difference is significant??and it's much greater in males. Conclusion    There are some differences in the position of the mental foramen between the individuals of mandibular deviation deformity and the normal??and also are somewhat different between males and females. The CBCT imaging can clearly display the three-dimensional structure??the trend and the relationship with adjacent structures of the mental canal??which can effectively reduce or avoid the surgical complications.     

Clinical application of a new compact CT system to assess 3-D images for the preoperative treatment planning of implants in the posterior mandible A case report

When treatment planning before placing dental implants in the posterior region of the mandible, the locations of the inferior alveolar nerve and mental foramen need to be ascertained, as they determine the bone height available and the implant length selected. The purpose of this study was to introduce the clinical application of a newly developed compact computed tomography system (Ortho-CT) to assess three-dimensional (3-D) images for the preoperative treatment planning of implants in the posterior region of the mandible. To evaluate the 3-D images, we scanned using the Ortho-CT system the mandible with a radiopaque template placed in the posterior region. The Ortho-CT images provided excellent information for evaluating the morphology of the mandible, and for showing the location of the inferior alveolar nerve, mental foramen and the relationship of the template to the bone. We consider that Ortho-CT is a useful aid to preoperative treatment planning of implant therapy in the mandible.     

Studies of residual ridge resorption. Part I. Use of panoramic radiographs for evaluation and classification of mandibular resorption

This article describes a method of estimating the severity of mandibular bone resorption by using the mental foramen and the inferior border of the mandible, as they appear in panoramic radiographs, as reference points.Measurements of 260 images in panoramic radiographs of normal mandibles reveal that, in a high percentage of films, regardless of the usual magnification or distortion of the images, the lower edge of the mental foramen lies very close to a line dividing the mandible into thirds. By using the approximate ratio of 3:1, the original height of the mandible can be conveniently estimated from the height of the lower edge of the foramen above the inferior border of the mandible. The reduction in height of the bone can then also be estimated.It is suggested that this method of estimating and describing the degree of bone resorption may facilitate the study of this disease by providing an anatomic basis for classifying or grouping patients affected to varying degrees.     

A mathematical model for simulating the bone remodeling process under mechanical stimulus.

OBJECTIVES: Among the current mathematical models for bone remodeling, few can consider bone resorption due to overload. The objective of this paper is to develop a new bone remodeling model which can simulate both underload and overload resorptions that often occur in dental implant treatments. METHODS: Based on the traditional model, a new mathematical equation relating the density change rate with mechanical stimulus has been developed. The new equation contains an additional quadratic term which can produce reduction in bone density at high load levels. In addition, to fully exploit the characteristics of this model, a range of different bone remodeling behaviors were studied under the load cases with both constant and varying stress magnitudes. Finally, the model was applied in conjunction with the finite element method to a practical case of dental implant treatment. RESULTS: The FE analysis results showed that bone resorption at the neck of the implant occurred due to occlusal overload but then resorption stopped after some time before reaching the coarse threads. Meanwhile, the density of the bone deeper into the mandible increased slightly due to the additional mechanical stimulus provided by the occlusal load. This phenomenon is observable in some clinical situations. SIGNIFICANCE: The new model can describe the bone overload resorption, a feature which is absent in most of the current models. And by simulating the dental implant treatment using FE method, the ability of the new mathematical model to simulate overload bone resorption has been clearly demonstrated.     

Bone Remodeling of the Human Mandible during Prenatal Development

Material and Method: Based on histological serial sections of human fetuses (22-117 mm crown-rump length) the remodeling of the bone surfaces of the fetal mandible was characterized and visualized in 3D reconstructions. Results: In the embryo of 22 mm crown-rump length the mandible was completely covered by cells producing bone apposition, but beginning with the embryo of 25 mm crown-rump length, morphological differentiations of these cells leading to bone modeling were visible. These modeling processes were found to be much more complicated than described in the literature so far. Conclusion: Bone growth of the fetal mandible is a complex process comprising not only lingual resorption and buccal apposition. Instead, we found well differentiated remodeling processes, represented by variable portions of apposition, resorption and resting areas seamed by lining cells. Zusammenfassung Material and Methode: Die Umbauvorgänge an der Knochenoberfläche der menschlichen Mandibula während der vorgeburtlichen Entwicklung (22-117 mm Scheitel-Steiß-Länge [SSL]) wurden anhand von histologischen Schnittserien charakterisiert und nach 3-D-Rekonstruktion graphisch dargestellt. Ergebnisse: Im Embryo von 22 mm SSL wurde die Mandibula noch von zirkulär anbauenden Zellen umsäumt, doch bereits bei 25 mm SSL begannen morphologische Differenzierungen und damit Modellierungsvorgänge. Es zeigte sich, dass sie weitaus komplexer sind als bisher in der Literatur beschrieben. Schlussfolgerung: Das Knochenwachstum der fetalen Mandibula ist bereits ein komplexer Prozess, der nicht nur auf lingualer Knochenresorption und bukkaler Apposition beruht. Stattdessen liegen hier differenzierte Remodellierungsprozesse, bestehend aus räumlich und zeitlich variablen Anteilen von Apposition, Resorption und Ruhezonen, vor.     

Histoquantitation on small jaw specimens

ABSTRACT – A Study is carried out to evaluate the possibility of obtaining a measure of bone mass and bone activity by histoquantitation on small jaw specimens. The material consisted of bone autopsy specimens from premolar regions of mandibles and regions above maxillary second incisors. Microradiograms of 100-μm-thick buccal-lingual ground sections were used. Quantitation of bone mass (bone area in percent), bone coarseness (total bone surface/bone area), and bone activity (resorption surfaces/total bone surface) was done in well-defined areas of cortical and trabecular bone by an electronic point-counting system. The analysis indicates that: (1) no further information or accuracy is obtained from measurements of large areas than of small areas of cortical or trabecular bone, (2) the bone mass in the buccal cortex anterior to the mental foramen is independent of side and state of dentition, and (3) maxillary specimens are unsuitable for quantitation of bone mass. A small bone specimen taken anterior to the mental foramen seems to be suitable for histoquantitation, when a reliable and representative measure of bone mass and bone activity in the mandible is desired for analysis of intermandibular differences.     

Volume changes of autogenous bone grafts after alveolar ridge augmentation of atrophic maxillae and mandibles

The aim of the present retrospective chart review was to determine the relationship between nonvascularized osseous graft remodeling and the three-dimensional (3D) features of grafts and recipient sites, the anatomical recipient regions and different graft sources. 32 iliac crest or chin grafts were onlay-positioned in the mandible or maxilla of 14 patients. CT scans, taken before implant positioning and after 1 year, revealed a mean volume resorption of 35–51%. For iliac crest grafts, the average resorption was 42% when the onlay was positioned in the anterior maxilla and 59% when it was positioned in the posterior mandible. Spearman correlation and 3D interpolation analysis revealed, for both iliac crest groups, a moderate or advanced remodeling pattern depending on 3D features, namely graft thickness and shape, basal bone volume of recipient site, and the basal bone/graft volume ratio of the recipient site. No statistically significant differences were found between the recipient and donor site groups. Retrospective analysis of the data indicates that iliac crest grafts, onlay-positioned on adequate basal bone volume, may register a reduced volume remodeling when shaped thick in the anterior maxilla or rounded and convex, on the external surface, in the posterior mandible.     

Histoquantitation on small jaw specimens.

A study is carried out to evaluate the possibility of obtaining a measure of bone mass and bone activity by histoquantitation on small jaw specimens. The material consisted of bone autopsy specimens from premolar regions of mandibles and regions above maxillary second incisors. Microradiograms of 100-micrometer-thick buccal-lingual ground sections were used. Quantitation of bone mass (bone area in percent), bone coarseness (total bone surface/bone area), and bone activity (resorption surfaces/total bone surface) was done in well-defined areas of cortical and trabecular bone by an electronic point-counting system. The analysis indicates that: (1) no further information or accuracy is obtained from measurements of large areas than of small areas of cortical or trabecular bone, (2) the bone mass in the buccal cortex anterior to the mental foramen is independent of side and state of dentition, and (3) maxillary specimens are unsuitable for quantitation of bone mass. A small bone specimen taken anterior to the mental foramen seems to be suitable for histoquantitation, when a reliable and representative measure of bone mass and bone activity in the mandible is desired for analysis of intermandibular differences.     

Morphological study of unnamed foramina in north Indian human mandibles and its possible role in neurovascular transmission

The present study was undertaken to investigate the different unnamed foramina in the mandible, placing more emphasis on the foramen present on the medial aspect of the mandible near the last molar teeth. Macerated mandibles in 4% of cases showed the presence of foramen. These were investigated for their possible role in neurovascular transmission. The unnamed medial foramen and the incisive foramen may transmit fibres from the nerve to mylohyoid, to supply the lower last molars and incisors, respectively, thereby providing escape of pain fibres to these teeth after the inferior dental nerve block by the local anaesthesia at the mandibular foramen. Mandibles dissected along with the attached muscles showed transmission of blood vessels through the foramina present at the insertion of muscles.     

Effect of Ageing Towards Location and Visibility of Mental Foramen on Panoramic Radiographs

Mental foramen is an opening of the mental canal onto the lateral surface of the mandible. In this pilot radiographical study, in Malay population the effects of ageing towards the location and visibility of the mental foramen were determined. Most of the mental foramina were found to be located inferior to the apex of the second premolar. Non-visibility of the foramen was greatly increased in patients aged 50 years and above (Pearson Chi-square; p = 0.00). This finding may provide a guide to dental surgeries in Malay patients of different age groups.     

Lateral bone condensing and expansion for placement of endosseous dental implants: a new technique

Placement of endosseous dental implants can be a problem due to bone resorption if the patient has been missing teeth for a considerable period of time. In the literature, bone-grafting techniques have shown variable results. Additionally, bone grafting requires a longer treatment time and a need for a second surgery, and it adds significant cost to the treatment. These factors often discourage patients from having dental-implant treatment. Another technique for placement of dental implants in narrow bone ridges is repositioning and remodeling of alveolar bone by condensing and expansion with the help of bone osteotomes. This article presents 2 cases, 1 in the maxilla and 1 in the mandible, for placement of endosseous dental implants with the use of a new bone-expansion osteotome kit that utilizes a screw-type configuration for bone condensing and expansion.     

Relationship between mandibular cortical bone height and bone mineral density of lumbar spine

The aim of this study was to evaluate the association between lumbar spine bone mineral density and mandible cortical bone height at the mental foramen and at the angle of the jaw. PATIENTS AND METHODS: A total of 130 women living in Lithuania, were examined. None of the participants were known to have endocrine, metabolic or skeletal disorders. Bone mineral density (BMD) was measured in the spine lumbar area L2-L4. The mandibles were examined on panoramic x-ray images. On each radiograph cortical thickness of mandible was measured at the mental foramen and at the angle of the jaw. The results demonstrated a tendency of high probability of osteoporosis in cases were radiomorphometric parameters are low. There was a significant difference between bone mineral density of lumbar spine and cortical bone height of mandible below the foramen mentale and at the angle of the jaw (p<0.01).     

下颌正中管的锥形束CT成像研究

目的 通过锥形束CT（CBCT）对下颌正中管（MIC）的三维位置、走向及毗邻关系进行测量,为确保颏孔前区域牙种植手术的安全提供依据。方法 回顾80例患者的双侧下颌骨CBCT影像,对MIC的直径和毗邻关系进行测量分析,包括MIC至下颌下缘、下颌牙根尖、下颌骨颊侧壁和舌侧壁,以及双侧颏孔连线平面的垂直距离。结果 80例患者中,63例（占78.75%）的CBCT影像上可以观测到MIC影像,其管径大小为（1.21±0.29）mm。在垂直方向上,MIC距下颌下缘和下颌牙根尖的距离分别为（7.82±1.86）、（7.24±2.82）mm;在颊舌方向上,MIC距下颌骨颊侧壁和舌侧壁的距离分别为（3.80±1.37）、（4.45±1.34）mm;MIC距双侧颏孔连线平面的垂直距离为（5.62±2.21）mm。结论 CBCT通过多平面重建后,可以清晰显示MIC在下颌骨中的三维空间位置、走向及毗邻关系;利用CBCT 对MIC的位置和走行进行研究是可行的。     

Recent developments in interpositional bone-grafting of the atrophic mandible

A clinical study on 54 patients, who underwent augmentation of the atrophic mandible by interposed bone-grafts, but in whom routine follow-up vestibuloplasty was deliberately avoided, is presented. The results show a reduced rate of bone resorption in the anterior region and less interference with lip and chin sensibility. An additional study is included concerning the fate of the elevated ridge and associated bone-graft in the body region posterior to the mental foramen. Results suggest that the resorption pattern in this area is very similar to that of a subperiosteal bone-graft. Modification of surgical technique in this regard has produced encouraging results.     

Peri-implant Bone Remodeling Around an Extraction Socket: Predictions of Bone Maintenance by Finite Element Method

Purpose: The aim of this study was to investigate peri-implant bone remodeling as a response to biomechanical factors, including implant size and contour, magnitude of occlusal load, and properties of osteogenic bone grafts through the use of a computational algorithm. Materials and Methods: A bone-remodeling algorithm was incorporated into the finite element method, where bone remodeling takes place as a result of the biomechanical alteration caused by dental implant placement and continues until the difference between the homeostatic state and the altered state is minimized. The site-specific homeostatic state was based on a model consisting of a natural tooth. Three long (11-mm) implants and two short (5-mm) implants were investigated. A three-dimensional segment of the mandible was constructed from a computed tomographic image of the premolar region, and an extraction socket was filled with bone graft. Results: Generally, the extent of bone loss in the cortical region was greater and denser bone developed at both the implant crest and apex with increased occlusal loads. The areas between implant threads were prone to bone resorption. Bone graft materials that were relatively stiff and that had high equilibrium stimulus values appeared to cause increased bone loss. Conclusions: Short implants are better for conserving the mechanotransductive signaling environment of the natural tooth than long implants. Also, short implants are predicted to lead to less interfacial bone loss at high loads over the long term, while long implants are associated with a more consistent level of bone loss for different amounts of loading. It is also predicted that in the long term, bone grafts with relatively low elastic modulus lead to lower levels of interfacial bone loss.     

The relationship between the metacarpal index and the rate of mandibular ridge resorption

This study tried to determine whether a relationship exists between the degree of alveolar resorption of the edentulous mandible and the degree of osteoporosis, as expressed by the metacarpal index. Eighty patients were examined. Each had a radiograph of the left hand to show the second metacarpal, and a standard pan-oral radiograph. A morphological measurement of the metacarpal bone, which is a good indication of the mineral content of the skeleton, was made on each hand radiograph. Alveolar resorption was estimated on the pan-oral radiograph by taking the original height of the alveolar process as being three times the distance from the inferior border of the madible to the inferior edge of the mental foramen. The regression analysis revealed no relationship between osteoporosis, as measured by the metacarpal index, and the amount of alveolar bone resorption.     

Bisphosphonate effects on alveolar bone during rat molar drifting

The remodeling of bone during molar drifting and cortical growth in the rat maxilla and the effects of dichloromethylene bisphosphonate (Cl2MBP) on these processes were investigated in 30 age-matched rats. A control group of six rats was killed at 10 weeks of age. Beginning at 10 weeks of age, 12 rats were treated with daily subcutaneous injections of Cl2MBP (10 mg/kg), and 12 control rats were injected daily with normal saline. Six rats of each group were killed at 12 and at 20 weeks of age. All rats were injected with fluorescent bone labels eight and one days before termination. Calcified and decalcified vertical sections through the lingual roots of maxillary molars were prepared for histomorphometry. Bone apposition rates, remodeling activity, and bone cell populations were quantified by image analysis on depository and resorptive surfaces of alveolar bone and on cortical bone surfaces. The drift rates of the first and second molars were calculated. Results showed that in control animals the drift rate of the first molar exceeded that of the second molar (p less than 0.05), supporting a previously proposed mechanism for age-dependent narrowing of interdental bone. Cl2MBP treatment decreased remodeling activity on resorptive surfaces of alveolar bone, despite a transient increase in osteoclasts. Cl2MBP also decreased the osteoblast number and bone apposition rate on depository surfaces of alveolar bone, and reduced the rate of molar drifting (p less than 0.05). However, Cl2MBP treatment had no detectable effect on osteoblast number or bone apposition on cortical bone surfaces. These results support the concept that bisphosphonates influence bone formation indirectly through a coupling mechanism which links formation with resorption.